1. Field of the Invention
The present invention is directed generally to mounting frames and, more particularly, to a universal mounting frame for towing.
2. Description of the Related Art
Conventional tow trucks are designed to lift and tow a vehicle (e.g., an automobile) in a known manner. The disadvantage of a conventional tow truck is that it is specialized only for towing vehicles. Instead of tow trucks, specialized vehicles, such as a tractor trailer, are used to pull trailers for purposes such as transport of goods and other items. These specialized vehicles have a device known as a “fifth wheel” to permit coupling to a trailer in a conventional fashion. The trailer is equipped with a kingpin that mates with the fifth wheel. In normal operation, a significant downward force is applied to the fifth wheel by the weight of the trailer under tow and the contents, if any, of the trailer.
Past attempts have been made to provide a towing vehicle that is capable of operation as a normal tow truck (i.e., lifting and towing a vehicle) as well as operation with a fifth wheel. Such devices are disclosed by way of example in U.S. Pat. Nos. 5,823,735 and 6,036,428. In those references, a towing adapter is attached to the fifth wheel mounting plate of the tow vehicle. That is, an adapter is mounted on the tow vehicle and coupled to the tow vehicle's fifth wheel to permit the tow vehicle to operate as a conventional tow truck. This technique allows the tow vehicle to be used both for conventional towing and for towing a trailer via the fifth wheel.
The disadvantage of this technique is that the towing adapter allows an upward force to be applied to the fifth wheel. As previously noted, the fifth wheel is designed for operation with a trailer wherein the trailer applies a significant downward force to the fifth wheel. The fifth wheel is typically designed to accommodate this downward force and retain the trailer kingpin within the fifth wheel. However, when a towing adaptor is mounted to the tow vehicle via the fifth wheel, upward forces are applied to the fifth wheel. This is particularly true when the tow vehicle attaches to and lifts a vehicle under tow (e.g., an automobile). The weight of the vehicle under tow applies a significant downward force to the back of the towing adapter, which rests on the rear of the frame of the trailer. This downward force is applied through a moment arm to a pivot point in the towing adapter and translated to an upward force at the fifth wheel. The translation of these forces is similar to the forces applied to a teeter-totter where a downward force applied to one end of the teeter-totter is translated into an upward force at the opposite end of the pivot arm.
The fifth wheel is designed for operation with a trailer that exerts a downward force on the fifth wheel, but is not designed to accommodate such upward forces. The result is an undesirable upward force applied by the kingpin to the fifth wheel plate. To prevent such upward force, the device disclosed in the aforementioned patents includes a pair of link members coupled between the towing frame and the vehicle frame to resist upward force of the kingpin with respect to the fifth wheel plate.
The same approach is taken in a towing adapter widely sold by the Ernest Holmes Company, which manufactured a towing adapter mounted to the tow vehicle via the fifth wheel. In devices sold by Holmes, ratchet binders or chains and load binders are coupled between the tow frame and the frame of the tow vehicle to resist upward force of the kingpin at the fifth wheel plate.
Unfortunately, these conventional approaches involve expensive and lengthy assembly and potential risk of significant instability of the coupling between the kingpin and the fifth wheel unless extra steps are taken to mount link arms or ratchet binders to resist the upward force applied by the kingpin to the fifth wheel plate.